Cleats secured to footwear used in soccer, rugby, lacrosse, cricket, American football and other field sports have typically taken the form of individual replaceable hard plastic or metal studs that threadedly engage respective receptacles mounted in the outsole of an athletic shoe. Depending on player preferences and conditions, the studs typically range in length from ten millimeters to eighteen millimeters. For muddy and similar poor field conditions, longer studs are conventionally more desirable because they penetrate the ground more deeply to provide better traction. That is, it is the surface area of the stud in contact with the sod (i.e., the turf and top soil) below the ground level that engages the sod for traction during a push-off for a running step or during an attempt to stop. Therefore, more stud surface area makes contact with the sod as penetration into the sod increases. However, when studs penetrate the sod more deeply, the wearer is unable to run as fast as he/she would be able to when there is less penetration. For example, a 15 mm stud penetrates the ground only to approximately 10 mm on initial impact and, as the runner pushes off to take the next step, the downward force causes the stud to initially sink further toward the maximum 15 mm depth. This is referred to as secondary sink or penetration, the limitation of which is defined by the outsole of the shoe abutting the ground. The result of secondary penetration is a significant loss of power on the push off for each step, thereby limiting running speed. In addition, a not insignificant amount of the wearer's energy (i.e., force and time) is used in withdrawing a long stud from the muddy turf with each step.
Apart from the loss of push-off power, long studs are believed to cause many field sport injuries. The longer the stud, the more deeply anchored it becomes in the turf. When studs are deeply anchored, forces suddenly applied to ankles, legs and knees are more likely to create injuries since the stud and shoe cannot readily break away from the turf in response to sudden momentum changes of the runner and lateral impact from collisions and tackling. In other words, when the shoe does not easily break away from the turf, a portion of the leg is more likely to break or become sprained in response to lateral forces applied to a knee or leg.
It is known to provide golf shoes with plastic cleats that provide traction without penetrating the ground. This is a highly desirable characteristic for golf shoe cleats because ground penetration, particularly on putting greens, can damage the grass root system and leave uneven terrain that adversely affects the ability to accurately putt a golf ball. A highly efficient type of golf cleat for this purpose provides dynamic traction wherein traction elements on the cleat flex, typically spreading outwardly, under the load of the wearer's weight and, in doing so, provide the desired traction without ground penetration. Examples of dynamic traction cleats may be found, for example, in U.S. Pat. Nos. 6,209,230, 6,305,104 and 7,040,043, the disclosures of which are incorporated herein by reference in their entireties. In these patents, cleats are disclosed which take the form of a hub with a connector such as a threaded shaft extending from the hub top surface that can be selectively secured to a mating connector mounted in a golf shoe outsole. Plural flexible traction elements extend generally downward and outward from the hub periphery to frictionally engage the surface, become entangled with grass blades and turf, and trap grass blades against the shoe outsole, all of which combine to provide traction as the traction elements flex under the weight of the wearer. It is the flexure of the traction elements that give these cleats the name “dynamic traction cleats” and distinguish them from plastic cleats wherein the plural traction elements are inflexible, or “static”, and provide only the more limited traction resulting from direct point to point contact on the ground surface.
One approach to overcoming the aforementioned disadvantages of the conventional soccer stud is disclosed in U.S. Patent Application Publication No. 2009/0211118 (Krikorian et al, U.S. patent application Ser. No. 12/393,451) wherein dynamic traction is used to reduce secondary penetration by field studs into muddy and soggy sod. Specifically, the cleat comprises a hub, a stud of substantially non-flexible material extending downwardly from a lower surface of the hub, a cleat connector extending upwardly from an upper surface of the hub, and dynamic traction elements extending downwardly from the lower surface of the hub, typically from the hub rim, and adapted to flex upwardly when the cleat is connected to a shoe. The distal end of the stud is substantially flat or slightly rounded (e.g., beveled) and extends further from the lower surface of the hub than the distal end of each unflexed dynamic traction element such that, when the shoe to which the cleat is connected is forced downward toward the ground surface, the stud contacts and/or begins to penetrate the ground surface to provide initial traction before each dynamic traction element makes contact with the ground surface. The dynamic traction elements thus reduce the secondary penetration of the stud and eliminate some of the disadvantages described above.
We have found that even the initial penetration of the stud disclosed in Krikorian et al adversely affects the speed and quickness of the wearer of the shoe because of the effort required to remove the stud from that penetration. Moreover, even the initial penetration has been found to be undesirable from a safety/injury perspective for the reasons described. It would be desirable, therefore, to utilize dynamic traction in a field cleat without a penetrating stud.
Initially, in studying the above-stated problems, we conducted experiments involving attaching to field sport athletic shoes some commercially available versions of the dynamic traction cleats disclosed in U.S. Pat. Nos. 6,305,104 (available commercially as BLACK WIDOW® cleats under the SOFTSPIKES® brand) and 7,040,043 (available commercially as PULSAR® cleats under the SOFTSPIKES® brand). It was found in field sports tests that traction was not as reliable as desired because the dynamic traction elements did not efficiently entangle with and trap grass blades in response to sudden starts, stops and directional changes by the player wearing the shoe. Moreover, it was also discovered that the dynamic traction elements were becoming damaged in response to the shear and torsional stresses produced by those sudden momentum changes.
Further, in some instances the attachment between the cleat and the receptacle was compromised in response to sudden momentum changes. Specifically, the BLACK WIDOW and PULSAR cleats employ the very reliable FAST TWIST® locking system of the type disclosed in U.S. Pat. Nos. 6,810,608 and 7,107,708. In that system a circular array of locking posts are angularly spaced and uniformly arranged about the cleat hub. The receptacle is provided with a continuous ring of multiple adjacent locking teeth of generally triangular configuration such that the apices of successive teeth click past the interfering locking posts and then more firmly engage the locking posts as the threaded engagement between the cleat and receptacle is tightened (i.e., as the threaded cleat stem is rotated further into the threaded receptacle socket). Although this arrangement functions perfectly when used in golf shoes, we found that the engagement between the posts and teeth is often compromised when subjected to the stresses of sudden starts, stops and turns experienced by shoes used in field sports.
It is desirable, therefore, and an object of the invention, to provide a cleat and cleat receptacle that utilize dynamic traction effectively, reliably and safely when used in field sports shoes.